1. Field of the Invention
This disclosure relates to servicing a wellbore. More specifically, it relates to servicing a wellbore with sealant compositions comprising a calcium aluminate cement and a gelation inhibitor and methods of using same.
2. Background of the Invention
Natural resources such as gas, oil, and water residing in a subterranean formation or zone are usually recovered by drilling a wellbore down to the subterranean formation while circulating a drilling fluid in the wellbore. After terminating the circulation of the drilling fluid, a string of pipe, e.g., casing, is run in the wellbore. The drilling fluid is then usually circulated downward through the interior of the pipe and upward through the annulus, which is located between the exterior of the pipe and the walls of the wellbore. Next, primary cementing is typically performed whereby a cement slurry is placed in the annulus and permitted to set into a hard mass (i.e., sheath) to thereby attach the string of pipe to the walls of the wellbore and seal the annulus. Subsequent secondary cementing operations may also be performed.
Wellbore servicing fluids are often modified to allow them to function for their intended purpose under extreme conditions (e.g., high temperatures, acidic environment). For example, when cementing high temperature wells, such as steam injection wells or steam production wells, calcium aluminate cements (CACs) are typically used. In such wells, the higher temperature resistance of CACs compared to Portland cement/silica mixtures is an advantage for long term integrity of the cement sheath. The use of CACs offers many advantages as they provide in addition to high temperature resistance, low temperature resistance, sulfate resistance, corrosion resistance and sour gas resistance. Additional examples of wellbore servicing that typically employ CACs include geothermal wells or carbon dioxide injection wells. At high static subterranean temperatures, and in the presence of brines containing carbon dioxide, conventional hydraulic cements rapidly deteriorate due to alkali carbonation and the use of conventional hydraulic cement compositions in these types of wells may result in the loss of wellbore integrity.
CACs combined with a soluble phosphate salt, for example sodium metaphosphate and a filler such as Class F flyash, form quick setting cement that upon setting binds well to the subterranean formation and to itself and has desirable mechanical properties such as high strength, carbonation resistance and low permeability. These compositions are described in Journal of Material Science, 32, 3523-3534 (1997) and J. Material Science, 37, 3163-3173 by Sugama et al, and in U.S. Pat. Nos. 5,900,053, 6,143,069 and 6,332,921 issued to the assignee of the current invention, each of which is incorporated by reference herein in its entirety.
A variety of CACs are commercially available with alumina contents that can range from about 40% to about 80% by weight of the composition. Additionally, these CACs may have iron oxide present in amounts of 18% or higher by weight of the composition. While attractive from an economic standpoint, a significant drawback to the use of low alumina and/or high iron oxide CACs is their tendency to prematurely gel. Furthermore, premature gelation may be exacerbated by other components commonly used in cement slurries and/or may vary depending on the source of the components. As such, premature gelation of cementitious slurries comprising a low alumina and/or high iron oxide CAC along with unpredictable thickening times make well cementing with these types of CACs a challenge. A need therefore exists for materials that prevent the premature gelation of CACs having a low alumina and/or high iron oxide content.